Silicosis and lung cancer: A mortality study of a cohort of silicotic workers in Hong Kong

Purposes. To describe the pattern of mortality in a cohort of silicotic workers in Hong Kong, comparing to the general population; to examine the relationship between silicosis and lung cancer, after taking into account the effect of smoking and excluding the influence of other possible occupational lung carcinogens; to elucidate the joint effects of smoking and silicosis on the risk of lung cancer; and to explore the exposure-response relationship between different indices of silica dust and mortality from lung cancer.;Methods. A retrospective cohort study was designed. A total of 2789 male silicotic workers assessed at the Pneumoconiosis Clinic of the Department of Health during the period of 1981 to 1998 were followed up through the end of 1999 to ascertain the vital status. The standardized mortality ratios (SMR) were calculated, for total and major causes of death using the male general population in Hong Kong as the external reference. Axelson's method was used to indirectly adjust for the confounding effect of cigarette smoking on the association of silicosis with the risk of lung cancer. The joint effect of smoking and silicosis on lung cancer was also examined. The multivariate Cox's proportional hazard regression model was applied to examine the exposure-response relationship between silica dust exposure and the risk of lung cancer.;Conclusion. Findings from this cohort study suggested that silicotic workers had a much higher mortality from non-malignant respiratory diseases than the general population. The death of esophagus cancer increased significantly among silicotics, especially among those in caisson dusty trade. There was a weak but elevated risk of lung cancer among silicotic workers after taking into account the effect of smoking and excluding other concomitant occupational lung carcinogens. The effect of silicosis on the risk of lung cancer in nonsmokers was stronger than that in smokers. There was no consistent exposure-response relationship between the mortality of lung cancer and silica dust exposure in this cohort. Our results provided some positive evidence to support the decision by the International Agency for Research on Cancer (IARC) to classify inhaled silica dust in occupational settings as a human carcinogen. (Abstract shortened by UMI.).